Water treatment and steam generation system for enhanced oil recovery and a method using same

ABSTRACT

A system of generating steam from an emulsion stream produced from a reservoir via thermal recovery has a heat exchanger for adjusting the emulsion to a first temperature; at least one separation device for separating water from the emulsion at the first temperature to obtain produced water; an optional produced water preheater, and a high pressure evaporator for receiving the produced water and generating steam using the produced water. The evaporator has a vapor drum; a heating element receiving the water stream, and in fluid communication with the vapor drum via a pressure letdown device; a heating source for imparting sensible heat to the water stream for generating steam. The evaporator also includes a recirculation pump for circulation of blowdown concentrate, and a bubble generator for generating bubbles and injecting generated bubbles into the heating element to enable self-removal of scales and other solid deposits in the evaporator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/215,714, filed on Jul. 21, 2016, and claiming priority toCanadian patent application Ser. No. 2,956,159, filed on Jan. 25, 2017,the contents of both of which are incorporated herein by reference intheir entirety.

FIELD OF THE DISCLOSURE

The present invention relates generally to a water treatment and steamgeneration system, and in particular, to a water treatment and steamgeneration system for enhanced oil recovery, and a method for usingsame.

BACKGROUND

Hydrocarbon resources, such as oil, sand, or bituminous sand deposits,are found predominantly in the Middle East, Venezuela, and WesternCanada. The Canadian bitumen deposits are the largest in the world andare estimated to contain between 1.6 and 2.5 trillion barrels of oil.

Bitumen is heavy, black oil which cannot be readily pumped from theground due to its high viscosity. As is well known in the art,bituminous sands can be extracted from subterranean reservoirs bylowering the viscosity of the hydrocarbons in-situ, thereby mobilizingthe hydrocarbons such that they can be recovered from the reservoir.Many thermal-recovery processes, such as Steam Assisted Gravity Drainage(SAGD), have been developed to reduce the viscosity by application ofheat, chemical solvents, or combinations thereof, and to mobilize theviscosity-reduced hydrocarbons for better recovery. Such recoveryprocesses typically involve the use of one or more “injection” and“production” wells drilled into the reservoir, whereby a heated fluid(e.g. steam) can be injected into the reservoir through the injectionwells and hydrocarbons can be retrieved from the reservoir through theproductions wells.

The fluid produced from the reservoir is usually a mixture of oil andwater i.e., an emulsion. The emulsion is first processed for oil/waterseparation in a central processing facility (CPF). Bitumen separatedfrom the emulsion is transported to offsite facilities for furtherprocessing. Water separated from the emulsion is de-oiled, treated andrecycled within the CPF for steam generation and reinjection. CommercialSAGD plants in Alberta, Canada typically recycle more than 90% of thewater from emulsions for use in steam generation.

Traditionally, in order for the water retrieved during theseparation/de-oiling processes to be reused, recycled, and/orreinjected, the retrieved water must go through the following two steps:

a) water softening, via a standard atmospheric pressure evaporator orwater softener (using lime softening and ion exchange), wherein eachprocess option requires energy-intensive cooling of the de-oiled water,and

b) steam generation via a drum boiler or alternatively, an once-throughsteam generator (OTSG) wherein the cooled water is heated again togenerate steam.

Typically, existing evaporators are forced-circulation mechanicalvapor-compression evaporators comprising a vapor drum with vertical orhorizontal heating tubes and auxiliary equipment such as amechanical-vapor compressor, recirculation pumps, tanks, and exchangers.

For example and as will be described in more detail later, two watertreatment and steam generation technologies are generally known andavailable for commercial SAGD projects. One process uses lime softeningand ion exchange for treating produced water, followed by throughputthrough an OTSG boiler. The other process uses evaporation for treatingproduced water followed by heating in a drum boiler. Both processes usefired boilers to generate high-pressure steam and both processes requirewater treatment prior to the steam generation step.

These known processes are costly, time-intensive, energy inefficient,require significant operational care, and result in significant powerconsumption and consequently, in high levels of greenhouse gasemissions.

For example, the above-described processes are far from being energyefficient due to temperature variations, and/or phase changes along thewater path largely due to the contradicting process requirements beforeand after water softening, that including cooling the hot produced waterto prevent flashing in the atmospheric tanks or damaging the ionexchanges, and later heating softened water up to reserve boiler fuelconsumption.

SUMMARY

According to one aspect of this disclosure, there is disclosed a methodof generating steam from an emulsion stream produced from a reservoirvia thermal recovery. The emulsion stream is a mixture of oil and water.The method comprises: (i) adjusting the emulsion to a first temperature;(ii) obtaining produced water from the emulsion at the firsttemperature; and (iii) generating steam from the produced water at thefirst temperature.

In some embodiments, said first temperature is above 100° C.

In some embodiments, said first temperature is between about 100° C. andabout 250° C.

In some embodiments, said first temperature is between about 100° C. andabout 200° C.

In some embodiments, said first temperature is between about 140° C. andabout 150° C.

In some embodiments, obtaining said produced water from the emulsion atthe first temperature comprises: (i) separating water from the emulsionat the first temperature; and (ii) removing residual oil from theseparated water to obtain the produced water.

In some embodiments, removing said residual oil from the separated waterto obtain the produced water comprises removing residual oil from theseparated water by using at least two pressurized, high-temperature,induced-gas flotation units (IGF's) coupled in serial, to obtain theproduced water.

In some embodiments, generating said steam from the produced watercomprises: generating steam from the produced water at the firsttemperature by using a high pressure evaporator operating at a firstpressure.

In some embodiments, removing said residual oil from the separated waterto obtain the produced water further comprises: (i) using at least onepump to adjust the pressure of the produced water to the first pressure,and (ii) feeding the produced water to the high-pressure evaporator.

According to another aspect of this disclosure, there is provided asystem for generating steam from an emulsion stream produced from areservoir via thermal recovery. The emulsion stream is a mixture of oiland water. The system comprises: (i) a heat exchanger for adjusting theemulsion to a first temperature; (ii) at least one separation device forseparating water from the emulsion at the first temperature to obtainproduced water; and (iii) a high pressure evaporator for receiving theproduced water and generating steam using the produced water.

In some embodiments, a produced water preheater may be used forpreheating the produced water.

According to another aspect of this disclosure, there is provided anevaporator receiving a water stream and generating steam from the waterstream. The evaporator comprises: (i) a vapor drum; (ii) a heatingelement in fluid communication with the vapor drum; and (iii) a heatingsource for imparting sensible heat to the water stream for generatingsteam. The evaporator also includes a recirculation pump for forcedcirculation of blowdown concentrate from the vapor drum to the heatingelement, and a bubble generator for generating bubbles and injecting thegenerated bubbles into the heating element.

According to another aspect of this disclosure, there is provided anevaporator for receiving a liquid stream and generating steam from theliquid stream, the liquid stream comprising at least water. Theevaporator comprises: (i) a heating element comprising a liquid channelfor receiving the liquid stream, and a heating channel for directing ahigh-temperature heat-exchange medium therethrough to heat the liquid inthe liquid, (ii) a vapor drum for receiving the heated liquid from theheating element via a top connection pipe, and for generating steam fromthe heated liquid, the vapor drum comprising a steam outlet fordischarging generated steam, and a blowdown outlet for discharging ablowdown stream comprising un-vaporized liquid and impurities; and (iii)a bubble generator for generating bubbles using a gas-phase substance,injecting generated bubbles into the heating element for self-removal ofscales and other deposits in situ in the evaporator.

The removal of scales and other solids is achieved through fluidizationand cavitation effects of the injected bubbles in situ in theevaporator, i.e., the removal of scales and other solids occurs insidethe evaporator at the location where the solids formed, and when theevaporator is in operation.

In some embodiments, a heating source is used to directly heat aheat-exchange medium. The heated heat-exchange medium is circulated intothe heating channel of the evaporator for heating the liquid therein.

In some embodiments, the heat-exchange medium for imparting sensibleheat to the water stream is a hot oil or a synthetic heat-exchangemedium.

In some embodiments, the heating source may be a solar power collector.

In some embodiment, the heating source may be a fired heater.

In some embodiments, the heating source may be a solar power collectorand a secondary heater, such as a fired heater. The solar powercollector and secondary heater may be in either a serial arrangement ora parallel arrangement. The secondary heater may be used forcompensating for the solar power for heating up the heat-exchange mediumof the high pressure evaporator.

In some embodiments, the liquid channel comprises one or more verticalheating tubes for receiving water injected therein, and the heatingchannel receives heat-exchange medium heated by the heating source forimparting sensible heat to the water in the one or more heating tubes.

In some embodiments, an optional produced water preheater, e.g., anacross exchanger, is provided before the evaporator for pre-heating theproduced water feed from the first temperature using the heat-exchangemedium. The heat-exchange medium thus leaves the across exchanger with alowered temperature.

Hereinafter, an optional device or component means that such a device orcomponent may be used in some embodiments, but otherwise not be used insome other embodiments, depending on the implementation.

For example, the produced water preheater is described above as anoptional device, which means that in some embodiments, the system maycomprise a produced water preheater. However, in some other embodiments,the system may not comprise such a produced water preheater.

While the produced water preheater is optional, using such a producedwater preheater can improve energy conservation.

In some embodiments, the bubble generator uses non-condensable gas suchas pipeline natural gas for generating bubbles for removing scales andother solids in situ in the evaporator. Non-condensable gas remains inequilibrium with the high-pressure steam thereafter and flows to thereservoir for the non-condensable gas co-injection.

In some embodiments, the bubble generator uses solvent vapor from asolvent vaporizer for generating bubbles for removing of scales andother solids in situ in the evaporator. Solvent remains in equilibriumwith the high-pressure steam thereafter and flows to the reservoir forthe solvent-assisted extraction.

In some embodiments, the evaporator further comprises: a condenser forreceiving a portion of generated steam and condensing received steam towater. The bubble generator receives the condensed water discharged fromthe condenser and mixes the non-condensable gas or solvent vapor withthe received water for generating a water stream with gas bubbles forfeeding into the heating element.

In some embodiments, the motive water used for mixing thenon-condensable gas, or solvent vapor for bubble generation is from awater source that is external to the high-pressure evaporator.

In some embodiments, the motive water used for mixing thenon-condensable gas, or solvent vapor for bubble generation is obtainedfrom the evaporator's blowdown stream.

In some embodiments, the bubble generator is a sparger.

In some embodiments, the bubble generator is a bubble pump.

In some embodiments, the bubble generator is an eductor.

In some embodiments, the connection pipe between the vapor drum andheating element comprises a pressure letdown device, such as athrottling valve, an orifice, a converging diffuser, or a convergingpiping fitting, to withhold water in the bubble-mixed feed from flashinguntil it enters the device, where bubbles therein are squeezed tocollapse, creating cavitation for self-removal of scales and othersolids in situ in the connection pipe. This technique confines theevaporation-induced scaling to the top connection pipe, andsimultaneously removes the scale precipitates in the pipe.

In some embodiments, said vapor drum further comprises a steam/liquidinterface maintained at a level above its inlet piping system includingthe pressure-letdown device to allow flashing feed water into bulkliquid to further reduce the entrance turbulence and therefore, thenucleation scaling. The submerged entry also reduces salting as nosupersaturation is generated during flashing.

In some embodiments, said steam/liquid interface is maintained forseparating impurities from the produced steam, thereby forming theblowdown stream.

In some embodiments, the evaporator further comprises a recirculationpump for forced circulation at least a portion of the blowdown streaminto the liquid channel of the heating element.

The blowdown recirculation pump may comprise an optional blowdownrecirculation cooler in embodiments wherein the constructability of theblowdown recirculation pump is limited and cannot match the operatingtemperature of the evaporator.

In some embodiments, the evaporator also comprises a crystallizer forfurther concentrating at least a portion of the blowdown stream andrecovering the distillate.

In some embodiments, said crystallizer comprises at least one of aheating element, a flash drum, a sludge recirculation pump, a steamcondenser, a condensate sub-cooler, and a transfer pump.

In some embodiments, the crystallizer is used for injecting bubbles intothe crystallizer's heating element for removal of scales and othersolids through fluidization and cavitation effects in situ in thecrystallizer.

In some embodiments, the optional blowdown recirculation cooler may be apart of a plant-wide heat integration cycle using the heat-exchangemedium to eliminate the second heat transfer fluid such as glycol andother utility equipment.

In some embodiments, the heat-exchanger medium, after flowing out ofwith the heating element, flows through the crystallizer and an inletemulsion cooler in sequence, and flows into the optional blowdownrecirculation cooler before being heated by the heating source.

In some embodiments, the hot heat-exchange medium, after flowing out ofwith the heating element, first gives up heat to the crystallizer andother process heaters arranged in parallel with the crystallizer. Then,the temperature-reduced heat-exchange medium collects heat from theinlet emulsion cooler and other coolers arranged in parallel with theinlet emulsion cooler before being heated by the heating source.

In some embodiments, said other process heaters arranged in parallelwith the crystallizer include at least one of the above-describedproduced water preheater, the above-described solvent vaporizer, and aRankline cycle power generator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a prior-art three-stage, WLS-OTSG watertreatment and steam generation process for enhanced oil recovery;

FIG. 2 shows the devices and detailed process of the phase separationstage of the WLS-OTSG process of FIG. 1;

FIG. 3 shows the devices and detailed process of the water softeningstage of the WLS-OTSG process of FIG. 1;

FIG. 4 shows the devices and detailed process of the steam generationstage of the WLS-OTSG process of FIG. 1;

FIG. 5 is a schematic diagram of another prior-art three-stage,evaporator-drum boiler water treatment and steam generation process forenhanced oil recovery;

FIG. 6 shows the devices and detailed process of the phase separationstage of the evaporator-drum boiler process of FIG. 5;

FIG. 7 shows the devices and detailed process of the water softeningstage of the evaporator-drum boiler process of FIG. 5;

FIG. 8 shows the devices and detailed process of the steam generationstage of the evaporator-drum boiler process of FIG. 5;

FIG. 9 is a schematic diagram of a two-stage water treatment and steamgeneration process for enhanced oil recovery, according to oneembodiment of this disclosure;

FIG. 10 shows the devices and detailed process of the phase separationstage of the process of FIG. 9;

FIG. 11 shows the devices and detailed process of the steam generationstage of the process of FIG. 9;

FIG. 12 is a schematic diagram of a prior-art forced circulation, risingfilm long tube vertical evaporator (FCRFLTV);

FIG. 13 is a schematic diagram of a high-pressure, gas inter-cyclic(GIC) evaporator having a sparger/pump assembly, according to oneembodiment of this disclosure;

FIG. 14 is a schematic diagram of a portion of the high-pressure, GICevaporator of FIG. 13, showing the circulation of bubble-mixed liquidbetween the heating element and the vapor drum;

FIG. 15A is a schematic diagram of a high-pressure GIC evaporator havinga bubble pump and using condensed steam for bubble generation, accordingto an alternative embodiment of this disclosure;

FIG. 15B is a schematic diagram of high-pressure GIC evaporator using anexternal water source for bubble generation, according to yet anotherembodiment of this disclosure;

FIG. 15C is a schematic diagram of high-pressure GIC evaporator andusing the blowdown circulation and the solvent vapor for bubblegeneration, according to still another embodiment of this disclosure;and

FIG. 16 is a plant-wide heating and cooling medium system of the processof FIG. 9, according to one embodiment of this disclosure.

DETAILED DESCRIPTION

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs.

As used in the specification and claims, the singular forms “a”, “an”and “the” include plural references unless the context clearly dictatesotherwise;

The terms “comprising”, and “including” as used herein, will beunderstood to mean that the list following is non-exhaustive and may ormay not include any other additional suitable items, for example one ormore further feature(s), component(s) and/or ingredient(s) asappropriate.

The term “Steam Assisted Gravity Drainage” and its abbreviation of“SAGD” as used herein, will be understood to mean all thermal in-situproduction and processing oil methods including Cyclic Steam Stimulation(CSS), and/or other enhanced thermal exploration, production andprocessing methods with or without solvent(s) and non-condensable gasesco-injection, in the scope of this disclosure.

The term “fouling” as used herein, is interchangeable with salting, andscaling.

The term “warm lime softener” and its abbreviation of “WLS” as usedherein, will be understood to mean all the lime softening process,including hot softener which has an abbreviation of “HLS”.

The term “high pressure” and its abbreviation of “HP” as used hereinwill be understood to mean the pressure of 300 psig (2,069 kPag) andabove. The term “low pressure” and its abbreviation of “LP” will beunderstood to mean the pressure between 15 psig (103 kPag) and 100 psig(690 kPag). The term “atmospheric pressure” and its abbreviation of “AP”will be understood to mean the pressure between vacuum and 15 psig (103kPag).

In the following, there is disclosed a system and a method in watertreatment and steam generation for SAGD and/or other thermal in-situ oilapplications. The system disclosed herein may provide significanteconomic and environmental benefits.

The system disclosed herein focuses on both cost and energy efficiencyto make thermal in-situ oil projects less capital intense, more energyefficient and more renewable energy friendly. The system iscost-efficient as the disclosed GIC evaporator accepts low-quality feedwater from a leaner method for high-pressure steam generation.

The system disclosed herein is energy efficient as it eliminatesunnecessary temperature variation and/or phase changes along the waterpath as characterized in prior arts. The system is a high-temperature,pressurized system enabling water treatment and steam generation in onestep directly from the de-oiled produced water using a high-pressurefouling-resistant evaporator.

The disclosed system is also renewable energy integratable, capable ofusing solar energy for high pressure steam generation. The disclosedsystem may also integrate Rankline cycle power generation for on-sitepower generation.

The exponential increase in silica solubility at high temperature is thebase for the one-step steam generation process disclosed herein.

As is known in the art, silica is undesirable and must be removed fromthe boiler feed water. In the existing practices, silica is eitherremoved with a lime softener, or in an atmospheric evaporator.

In the prior art where silica is removed in an atmospheric evaporator atabout 100° C., a large amount of caustic must be added to increase thepH of the solution to an excessive high value, e.g. greater than 13, forsuppressing silica precipitation. However, such practice promotescalcite scaling.

The process disclosed herein maintains a high temperature of nearly 300°C. in the evaporator. The increased solubility as the result of hightemperature can keep the silica in solution, at a lower pH tosimultaneously sequester scaling.

Steam generation takes place in a scaling-resistant evaporator system asdescribed below, in one step with no feed water softening, and with areduced caustic consumption.

While the disclosed water treatment and steam generation systemstreamlines temperature and pressure from oil/water separation andde-oiling to steam generation for higher energy efficiency, it alsoeliminates the need of any produced-water cooler between the treater andthe skim tank in prior art, along with the issues associated with thisequipment piece which is notorious for its severe fouling.

The system and method disclosed herein replace the traditional watersoftening and steam generation steps with a single step of steamgeneration using a high-pressure evaporator.

In some embodiments, the high-pressure evaporator disclosed herein is afouling-resistant evaporator, function at high pressure and temperature,and generates steam directly from the de-oiled produced water in onestep with no feed water softening.

The disclosed evaporator is based on a forced circulation, rising filmlong tube vertical (FCRFLTV) evaporator normally used in chemicalindustry. The disclosed evaporator adds fouling-resistant characteristicto FCRFLTV evaporators by introducing micro-bubbles for self-removal ofscales and other solids in situ in the evaporator.

The disclosed high-pressure evaporator is suitable for steam generationin the central processing facility (CPF) of a SAGD plant, or,alternatively, for satellite steam generation at a well pad.

For purposes of illustration and comparison, two prior-art watertreatment processes are first described.

FIG. 1 is a schematic diagram of a prior-art, three-stage watertreatment and steam generation process 100 for enhanced oil recoverysuch as SAGD. The process 100 uses warm lime softener (WLS) to treatwater in the emulsion 104 produced from a reservoir 102 through one ormore thermal wells, and a once-through steam generators (OTSG) togenerate high pressure injection steam. This process is denoted as aWLS-OTSG process.

In this embodiment, the emulsion 104 is a high-temperature (typicallybetween about 170° C. to about 180° C.), oil and water mixture producedfrom the reservoir 102 by thermal production, and usually contains somegas, solids and hardness/silica that may cause fouling in watertreatment devices. The process 100 separates water from the emulsion104, removes impurities (e.g., residual oil, gas, solids, hardness andsilica), and generates high pressure steam.

As shown in a first, phase separation stage 106, the emulsion 104produced from the reservoir 102 is processed by oil/water separation 112for separating gas, oil, and water. The gas and oil separated therefromare further processed using technologies known to those skilled in thisart.

Water 114 separated from the emulsion 104 usually still contains a smallamount of residual oil, and is further processed by de-oiling 116 toremove residual oil therein, thereby obtaining de-oiled water 118 (alsodenoted as produced water).

At a second water softening stage 108, the produced water 118 is fedinto a water-softening process containing a lime softener 120 and weakacid cations (WACs) or strong acid cations (SACs) 186 (see FIG. 3) forremoving silica and hardness therein, outputting softened water 122.

At a third steam generation stage 110, the softened water 122 is fedinto an OTSG boiler 124 for generating high-pressure (HP) steam 126,which may be injected into the reservoir 102 for oil production.

FIG. 2 shows the devices and detailed process of the phase separationstage 106 of the WLS-OTSG process 100, which are usually located in aCPF. As the emulsion 104 is a high-temperature oil and water mixture, itis first cooled down by an inlet cooler 142 (via, e.g., heat exchanging)to about 140° C. to 150° C., combined with diluent, and is then fed intoa three-phase separator 144 such as a free water knock-out (FWKO) unit,which separates the majority of water from the emulsion 104 usinggravity. The oil separated by the FWKO 144, still contains on somewater, is fed into a treater 146 for desalting and dewatering, therebygenerating an oil product (not shown) with impurity of less than 0.5%basic sediment and water (BS&W).

The water 145 and 147 discharged from the FWKO 144 and the treater 146,respectively, are at a temperature of about 140° C. to 150° C. The water145 and 147 are combined, and are further cooled by a produced-watercooler 148 to about 80° C. to 90° C. The cooled water 114 is thenprocessed for de-oiling 116.

In this example, the cooled water 114 passes through a skim tank 152, aninduced gas flotation (IGF) unit 156 and an oil removal filter (ORF) 162for removing oil and fine solids therein. Pumps, e.g., a transfer pump160, may be used for transferring water between de-oiling units 152, 156and 162. Each of the de-oiling units 152, 156 and 162 can remove about90% oil from its inlet water. The produced water 118 discharged from theORF 162 is stored in a produced water tank 164, and may be pumped by atransfer pump 166 from the produced water tank 164 to unit(s) in thewater-softening stage 108 for further processing.

FIG. 3 shows the devices and detailed process of the water-softeningstage 108 of the WLS-OTSG process 100. As shown, the produced water 118discharged from the produced water tank 164 (FIG. 2) is processed usinga warm lime softener (WLS) 120 and then in a weak acid cation (WAC) ionexchange unit 186 for removing silica and hardness, respectively.After-filter (AF) may also be used for lowering the water turbidity.Pump 184 may be used for transferring water from WLS 120 to WAC ionexchange unit 186. The treated or softened water 122 (also denoted asboiler feed water) discharged from the WAC ion exchange unit 186 isstored in a boiler feed water (BFW) tank 190, and may be re-heated byone or more cross-exchangers or heat exchangers 194 to a highertemperature before entering the steam generation stage 110 for steamgeneration. A low-pressure (LP) pump 192 is used to pump the boiler feedwater 122 through the heat exchangers 194, which heats the boiler feedwater 122 using low-grade heat, and then feeds the heated water 122 intothe devices of the steam-generation stage 110 via a high-pressure (HP)pump 196.

FIG. 4 shows the devices and detailed process of the steam generationstage 110 of the WLS-OTSG process 100. In this example, progressiveheating is used, and as shown, the boiler feed water 122 is firstpre-heated, by a heat exchanger 202 using high grade heat to about 180°C. to 190° C. The heated water 122 is then fed into an OTSG 124 togenerate wet steam 204. The OTSG 124 can produce about 80% wet steam andabout 20% blowdown (comprising un-vaporized liquid and impurities suchas solids) based on treatment of a typical produced water withpreviously-described lime softener process 108, and must be followed byequipment to further separate blowdown for dry steam. In the exampleshown in FIG. 4, the wet steam 204 is fed into a high-pressure steamseparator 206, which generates high-temperature, high-pressure (HP)steam 126 for injection into reservoir 102 or oil wells. Steam blowdown209 (typically at about 300° C. and usually containing some impurities)from the HP steam separator 206 is fed back to the heat exchanger 202,thereby transferring heat to the boiler feed water 122. After heatexchange, the temperature-reduced steam blowdown 209 is fed to ablowdown cooler 210 to be cooled down for recycling and disposal.

While FIG. 4 shows a single-stage, high-pressure steam separator 206,multi-stage steam separation may be required when an improved waterrecycle rate is needed, and/or when a low pressure steam is needed for ahot lime softener.

The above prior-art system 100 has several drawbacks. For example, oilcontamination to the WLS 120 and the WAC ion exchange unit 186 can becostly because of the mass cleaning thereof, loss of production and/orequipment damage. Therefore, de-oiling 116 in the phase separation stage106 is designed as a three-step process involving three units, i.e., askim tank 152, an IGF 156 and an ORF 162, to provide necessaryredundancy for safeguarding the WLS 120 and the WAC ion exchange unit186 from oil contamination. Such multi-step de-oiling 116 causes highcost in equipment and operation.

Another drawback in the phase separation stage 106 is the low energyefficiency, as the produced water must be cooled down in theproduced-water cooler 148 from about 140° C. to 150° C. to about 80° C.to 90° C., and then later heated to about 180° C. to 190° C. after watersoftening 108, thereby wasting energy in this cooling-down/heating-upcycle.

Further, the produced-water cooler 148 is required in the aboveprior-art system 100 to prevent hot water 140 and 142 discharge fromFWKO 144 and the treater 146, respectively, from flashing into the skimtank 152 (FIG. 2) or to prevent melting the WAC ion exchange 186 (FIG.3). However, the produced-water cooler 148 in the system 100 has strongtendency of fouling, and a good fouling prevention solution is yet to befound.

The above-described water softening process 108 had been dominant inAlberta, Canada, until a directive became effective to optimize waterrecycle efficiency and make up water sources. Depending on the producedwater chemistry, this process may not be able to meet the requiredrecycle unless a backend evaporator, another OTSG, or equivalent is alsoutilized.

The above-described water softening process 108 also requires a largenumber of equipment resulting in high capital cost, and requires largeenvironmental footprint. The water softening process 108 causessubstantial energy and greenhouse gas emission due to frequent watertransfers including recycle, backwash, regeneration, and rinse. Theprocess 108 requires a substantial amount of chemicals and skilledoperators with a high level of operational attention.

As described above, in the event of oil channeling in the de-oiling 116,the produced water 118 fed into the water softening process 108 cancontain substantial amount of oil, causing contaminations in WLS 120,WAC ion exchange unit 186 and the OTSG 124.

FIG. 5 is a schematic diagram of another prior-art, three-stage watertreatment and steam generation process 300 for enhanced oil recovery.The process 300 uses evaporator and drum boiler, and is denoted as anevaporator-drum boiler process. The evaporator-drum boiler process 300recently becomes more popular due to the tightened regulation in watermanagement.

The process 300 is similar to the process 100 of FIG. 1 except that theprocess 300 uses an atmospheric pressure (AP), front-end evaporator 320for water softening 108, and a drum boiler 324 for steam generation 110.Accordingly, some devices used in the process 300 are different fromthose of the process 100.

FIG. 6 shows the devices and detailed process of the phase separationstage 106 of the process 300 which are usually located in a CPF. Asseen, the phase separation 106 of the process 300 is similar to that ofthe process 100 except that in the process 300, de-oiling 116 is atwo-step process using a skim tank 152 and an IGF 156. No ORF isrequired.

The omission of ORF benefited from the use of the AP front-endevaporator 320 in the water softening stage 108 which is less sensitiveto oil contamination in the produced water 118 and thus, does notrequire high-level de-oiling.

FIG. 7 shows the devices and detailed process of the water softeningstage 108 of the process 300. As shown, the produced water 118 is fedinto a forced circulation (FC) thermo-compression front-end evaporator320.

Many front-end evaporators are forced circulation, mechanical vaporcompression evaporator packages comprising a vapor drum with vertical orhorizontal heating tubes, and requisite components such as a feed tank,a deaerator, a feed/distillate exchanger, a mechanical vapor compressor,recirculation pumps, a distillate pump, a brine pump, and the like.

To ensure proper working of the evaporator 320, it is necessary tocondition and remove O₂, CO₂ and SO₂ from the produced water 118 toprotect the evaporator from corrosion or fouling. In many cases, theevaporator package is supplied with its own conditioning tank anddeaerator. In other cases, the produced water tank 164 upstream of theevaporator 320 is used as the conditioning tank.

Front-end evaporators 320 are often used when no disposal well isavailable or when a producer cannot obtain the required produced waterrecycle efficiency (which may be otherwise produced using the process ofFIG. 1). Comparing to the WLS-OTSG process 100, a large front-endevaporator 320 followed by a drum boiler 324 costs less than adding abackend evaporator to the process 100.

The evaporator 320 uses distillation to separate water from impurities.The distilled water 122, i.e., softened water, is discharged from theevaporator 320 into a boiler-feed water (BFW) tank 346 for storage. Thesludge 344 which comprises impurities and some water, is transferredinto a FC crystallizer 348, which may comprise necessary components suchas a vapor body, a mechanical vapor compressor, a recirculation pump, aheat exchanger and the like. The FC crystallizer 348 further separateswater from impurities, discharges separated water 326 to the BFW tank346 for storage, and discharges concentrated sludge 350 for disposal.

The softened water 328 in the BFW tank 346 may be pumped via alow-pressure (LP) BFW pump 352 and a HP BFW pump 354 to the drum boiler324 (see FIG. 5) for steam generation.

FIG. 8 shows the devices and detailed process of the steam generationstage 110 of the process 300. As shown, the boiler feed water 122 is fedinto a drum boiler 324 to generate HP steam 126 for injection intoreservoir 102 or oil wells. As is known in the art, drum boiler 324 is a“water tube” boiler with water on the tube side for high-pressure steamgeneration, typically in the range of 7,000-9,000 kPag. The drum boiler324 has tendency of fouling and requires high-purity boiler feed water122 that may be obtained by evaporation, and which may not be obtainablevia chemical treating of produced water.

Injection wells can tolerate small amounts of liquid in the injectionsteam without compromising the measurement, accounting, reporting, andother regulatory requirements. This allows the continuous blowdown 372to be re-combined with the dry HP steam for a wet-injection stream whilethe intermittent blowdown 374 is flashed into an AP flash drum 376 tofurther reduce its volume. The flashed vapor 378 is discharged in to theatmosphere in the form of vapor, and water 380 is discharged into theplant open-drain system. There are negligible impurities in water 380because of the high-quality distillate nature of boiler feed water 122.

In some situations, the process 300 may comprise two evaporators 320coupled in series, which are followed by a single crystallizer 348.

The process 300 also has several drawbacks. For example, while the drumboiler 324 has higher working pressure, larger capacity, and is moreefficient comparing to the OTSG, its initial cost is high.

The initial cost of the front-end evaporator 320 is also quite highbecause of the required large surface areas and the number of auxiliaryequipment. While the energy efficiency of the front-end evaporator 320is high due to the latent heat reuse and good heat transfer, the overallenergy efficiency of the system 300, however, is lowered because ofcyclic phase changes. The distillates condensed from the steam vapor inthe evaporator 320 need to be re-evaporated in the drum boiler 324.Compared to the process 100 using WLS 120 and WAC ion exchange unit 186,the total cost of the evaporator-drum boiler process 300 may be merelymarginally lower, but the greenhouse gas emissions of the process 300are much higher.

FIG. 9 is a schematic diagram of a two-stage water treatment and steamgeneration process 400 for enhanced oil recovery such as SAGD, accordingto one embodiment of this disclosure. The process 400 disclosed hereinis simple and energy efficient. Compared to the prior-art processes 100and 300, the process 400 does not comprise any water-softening stage.

As shown, the emulsion 104 produced from the reservoir 102 is firstprocessed at a phase separation stage 106 to obtain produced water 118from the emulsion 104. The produced water 118 is then directly fed intoan HP evaporator 424 in the steam generation stage 110 for steamgeneration. In other words, the process 400 uses the HP evaporator 424and a pressurized system to generate HP steam 126 directly from theproduced water 118. The water-softening stage is thus eliminated, and asimplified de-oiling process 116 is used to supply high-temperature,high-pressure water to the evaporator 424.

FIG. 10 shows the devices and detailed process of the phase separationstage 106 of the process 400, which are usually located in a CPF.

As shown, an inlet heat exchanger 402 is used to first adjust theemulsion 104 to a process temperature sufficiently high to maintainsilica dissolved therein, to achieve the best separation efficiency inthe downstream FWKO 144 and treater 146.

In various embodiments, the process temperature is set based on variousfactors such as the viscosity and specific gravity profiles of theemulsion 104, the treating method (e.g., dilute treating or flashtreating process), and the like. In some embodiments, the inlet heatexchanger 402 adjusts the emulsion 104 to a process temperature above100° C. In some other embodiments, the inlet heat exchanger 402 adjuststhe emulsion 104 to a process temperature between about 100° C. andabout 250° C. In yet some other embodiments, the inlet heat exchanger402 adjusts the emulsion 104 to a process temperature between about 100°C. and about 200° C. In still some other embodiments, the inlet heatexchanger 402 adjusts the emulsion 104 to a process temperature betweenabout 140° C. and about 150° C.

In this embodiment, the emulsion 104 produced from the reservoir 102 isa hot oil/water stream, and the inlet heat exchanger 402 cools theemulsion 104 down to a process temperature between about 140° C. andabout 150° C., which is suitable for operation of traditional downstreamdevices such as FWKO 144 and treater 146, and is still sufficiently highto maintain silica in a dissolved state in the emulsion 104.

The temperature-adjusted emulsion identified using numeral 404, isdischarged from the inlet heat exchanger 402 and fed into a three-phaseseparator 144 such as a FWKO unit which separates the majority of waterfrom the oil and water mixture 104 using gravity. The oil 406 separatedby the FWKO 144, still containing some water, is fed into a treater 146for desalting and dewatering.

The separated water 145 and 146 discharged from the FWKO 144 and thetreater 146, respectively, are combined (identified using numeral 114)and processed by de-oiling 116 for removing residual oil from theseparated water 114.

The de-oiling 116 of the process 400 is simplified by using afirst-stage and a second-stage pressurized IGFs 436 and 438 coupled inseries for removing oil and fine solids therefrom. In this embodiment,both IGFs 436 and 438 are operated at about the same temperature as theFWKO 144 and the treater 146, e.g., between about 140° C. and about 150°C., thereby eliminating the produced-water cooler 148 used in theprocess 100 of FIG. 1.

Optionally, make-up water 442 may be supplemented into the second-stageIGF 438 from a make-up water tank 440 via a transfer pump 444, for thepurposes of supplying startup water, make-up water, and decouplingproduction from steam injection.

The produced water 118 discharged from the second-stage IGF 438typically has a pressure between 300 kPag and 500 kPag. The producedwater 118 is further pressurized to a higher pressure, e.g., betweenabout 6,000 kPag to 10,000 kPag, and is pumped to the HP evaporator 424in the steam generation stage 110 via an HP evaporator booster pump 446and an HP evaporator charge pump 448. In this embodiment, the HPevaporator charge pump 448 has a high net-positive suction head (NPSH)requirement, and requires a booster pump 446 to avoid cavitation.

In the de-oiling 116 of the process 400, both IGFs 436 and 438 canremove free or entrained oil to a level that does not cause severefoaming in the HP Evaporator 424. In contrast to the prior-art process100 or 300 (FIG. 1 or 5) wherein the feed water quality must meet theOTSG manufacturers' or the American Society of Mechanical Engineers'(ASME) guidelines for OTSG's/water tube boilers, the feed water to theevaporator merely needs to be sufficient for safe operation of theevaporator and the injection wells. Consequently, as will be describedin more detail below, the process 400 does not comprise any WLS, nor WACion exchange unit for silica and harness removals.

In addition to its primary function of de-oiling, the second-stage IGF438 may also serve as a mixing drum for removing the entrainednon-condensable impurities originating from the make-up water 442. Ifneeded, pre-conditioning chemicals (not shown) can be added to the inletof the HP evaporator booster pump 446 or the inlet of the HP evaporatorcharge pump 448. Such chemicals may include, but are not limited to,anti-foam agents, scale inhibitors, dispersants, and caustic sodasolutions.

Although not shown in FIG. 10, in an alternative embodiment for a flashtreating scenario, a heat exchanger (not shown) may be used to heat thehigh-pressure emulsion exiting the FWKO 144 in order to achieve aflashed oil specification of 0.5% BS&W in a high-temperatureinverted-flash separator.

FIG. 11 shows the devices and detailed process of the steam generationstage 110 of the process 400. The components shown in broken lines inFIG. 11 are optional components, that is, they may be used in someembodiments, and may be omitted and not used in some other embodiments.

As will be described in detail, the devices and process of the steamgeneration stage 110 produce high-pressure steam 126 directly from theproduced water 118. The associated blowdown-handling system, e.g. thecrystallizer 530, is also described herein, as they are inherentlyrelated.

The details about the fouling-resistant features of the evaporator (andthe crystallizer) will be described later in related to the GICevaporator, and thus are omitted from FIG. 11 and its relateddescription.

As shown in FIG. 11, the produced water 118 is fed into the heatingelement 502 of the HP evaporator 424, and is heated by hot heat-exchangemedium 506. The heated produced water 118′ is then flashed into a vapordrum 514 in which the high-pressure steam 126 is separated from theblowdown and is sent to reservoir 102 for injection.

The steam 126 from the HP evaporator 424 may still contain a smallamount of impurities that are saturated in the steam throughequilibrium. However, such small amounts of impurities would not causeoperational problems in the pipeline, nor would these cause thereservoir 102 to foul.

The blowdown containing un-vaporized water, falls to a lower portion ofthe flash drum 514 and splits, e.g., by using a pipe tee, into acirculation stream 517 and a blowdown discharge stream 516. Theconcentrated blowdown stream 516 is discharged from the vapor drum 514into the crystallizer 530 (described later). On the other hand, theblowdown circulation stream 517 is forced, e.g., pumped by a blowdownrecirculation pump 645, to circulate through the heating element 502 andreenters the vapor drum 514.

In particular, before entering the heating element 502, the forcedblowdown circulation 517 from the recirculation pump 645 is combinedwith the produced water 118, and the mixture is then fed into theevaporator's heating element 502, in which the mixture is heated beforeflashing into the vapor drum 502.

Although not shown in FIG. 11, those skilled in the art will appreciatethat a boiling-suppression device may be installed on the piping betweenthe heating element 502 and the vapor drum 514 to avoid boilingoccurring within the heating element 502.

As described above, the mixture of the forced blowdown circulation 517and the produced water 118 is fed into the heating element 502 and isheated therein by a hot heat-exchange medium 506, which may be asuitable hot oil.

In this embodiment, the heat-exchange medium 506 is heated by a heatingsource 507 to a high temperature, e.g., between about 240° C. and about400° C. The heating source 507 in this embodiment comprises a solarcollector 510, and may also comprise a secondary heating source such asa fired heater 508 for compensating for intermittent solar power. Inparticular, the fired heater 508 is automatically shut down when solarpower is sufficient for maintaining the heat-exchange medium 506 at adesignated temperature between about 240° C. and about 400° C. (e.g.,during daytime), and is automatically started when solar power isinsufficient (e.g., during nighttime and during daytime in overcastdays). When the fired heater is turned on, heating power thereof isautomatically adjusted to compensate for the solar power for maintainingthe heating-exchange medium to the designated temperature.

As shown in FIG. 11, the solar collector 510 is optional. Thus, in someembodiments, no solar collector 510 is used, and the heating source 507may only comprise a fired heater 508.

After heating the produced water 118, the temperature-reducedheat-exchange medium 518 flows out of the heating element 502 and ispumped via a heat-exchange medium pump 512, back to the heat source 507for re-heating.

In this embodiment, at least a portion of heat-exchange medium 518 isdiverted to the crystallizer heating element 521 and an optionalproduced water preheater 531, and then used therein as a heating source.

During steam generation, the solids and other impurities in the producedwater 118 are concentrated in the high-pressure evaporator 424, and thenin the crystallizer 530, which is essentially a second-stage evaporator.

The crystallizer 530 is equivalent to the crystallizer used in the watersoftening stage of the prior-art evaporator-drum boiler process 300 (seeFIG. 7), or the prior-art backend evaporator supplemental to the limesoftener-OTSG process (see FIG. 4).

Referring back to FIG. 11, a blowdown stream 516 from the evaporatorsvapor drum 514, e.g., about 5% to about 40% of feed, is discharged tothe crystallizer 530 for further concentrating the blowdown andrecovering the distillate. The crystallizer 530 is in direct fluidcommunication with the evaporator 424 through the vapor drum 514 of theevaporator 424 and the heating element 521 of the crystallizer 530.There is little pressure difference between the two vessels (i.e., thevapor drum 514 and the heating element 521).

In the crystallizer flash drum 520, low pressure steam 522 is separatedfrom the sludge and condensed in a condenser 526. The sludge falls tothe lower portion of the crystallizer flash drum 520 and splits into acirculation sludge stream 533 and a concentrated sludge stream 524.

The circulation sludge stream 533 is pumped by a sludge circulation pump525 and is combined with the blowdown discharge 516 to circulate throughthe heating element 521, in which the mixture is heated, and flash intothe crystallizer flash drum 520. The concentrated sludge stream 524 isdischarged from the crystallizer flash drum 520 as waste to, e.g., acentrifuge or disposal wells.

Although not shown in FIG. 11, those skilled in the art will understandthat a boiling suppression device may be installed on the piping betweenthe heating element 521 and the crystallizer flash drum 520.

The flashed steam vapor 522 is condensed in a steam condenser 526, andthe condensed steam is recycled back to the de-oiling system by acondensate transfer pump 527 for reuse as feed water to the highpressure evaporator.

In some embodiments, a portion of the condensed steam from the transferpump 527 may be further cooled in a condensate subcooler 529, andrecombined with the concentrated sludge stream 524 in an effort to forma colder sludge stream 528, e.g., at about 80° C. to about 90° C.,acceptable to the centrifuges (not shown), or the disposal wells.

In this embodiment, chemicals such as anti-foam agents, scaleinhibitors, dispersants, and caustic soda solutions may be added intothe de-oiling system 116, the high pressure evaporator 424 and thecrystallizer 530. However, most of the chemicals will be in the internalcirculation within the evaporator 424 and the crystallizer 530, andtherefore, the actual chemical consumption is lower compared to theprior-art systems.

Following is a description of a prior-art forced circulation rising-filmlong-tube vertical (FCRFLTV) evaporator for the purpose of illustration,which is followed by a description of a fouling-resistant HP evaporatoraccording to one embodiment of this disclosure is described, and thenfollowed by a comparison of this embodiment with the prior-art FCRFLTVevaporator.

FIG. 12 is a schematic diagram of a prior-art FCRFLTV evaporator 640,commonly used in, e.g., the chemical industry as a concentrator toproduce anhydrous chemical product. The FCRFLTV evaporator is notwell-suited for processing SAGD produced water.

In this prior art and its original (chemical) applications, asteam-slurry interface 648A is maintained in the vapor drum 642 abovethe heating element 604, to create a hydro-static head for boilingsuppression in the heating element 604.

Feed water solution 606 enters from the bottom of the heating element604, heated by hot heat-exchange medium 610, and starts to boil at theheating tube exits because of head loss. Flashing continues along thetop connection pipe 646 until the vapor drum 642.

Condensed vapor and un-vaporized liquid fall to a lower portion of thevapor drum 642 and accumulate therein. The accumulated liquid includingcondensed water, is discharged from the vapor drum 642, and splits intoa circulation stream 644 which is pumped by a recirculation pump 645back to the heating element 604 and a blowdown discharge stream 650.

When using such a prior-art, FCRFLTV evaporator 640 for processingproduced water, the flashing would produce fine scales, salts and othersolids, and quickly plug the evaporator 640 due to the high levels ofscaling compounds and excessive nucleation.

FIG. 11 is an exemplary illustration on how the FCRFLTV evaporator isused in steam generation and blowdown concentration. Neither theevaporator 424 nor the crystallizer 530 are expected to last long unlessthe fouling resistant features disclosed herein (see FIGS. 13 to 15C)are incorporated thereinto.

In the following, a new fouling-resistant evaporator is described inanother embodiment of the present disclosure. The fouling-resistantevaporator may be used for generating high-pressure steam from theproduced water that contains scaling compounds. The evaporator is immuneto a satisfactory extent, from fouling/salting/scaling at a largeevaporation-to-feed ratio of about 60% to about 80%.

FIG. 13 is a schematic diagram of an HP, gas inter-cyclic (GIC)evaporator 700 having a sparger/pump assembly, according to thisembodiment. The HP GIC evaporator 700 disclosed herein may be used asthe HP evaporator 424 in the process 400.

The disclosed evaporator alters the FCRFLTV evaporators by introducinghigh density bubbles to the heating element resulting in afouling-resistant evaporator capable of generating high-pressure steam.

As shown, the GIC evaporator 700 comprises an FCRFLTV evaporator 640 forsteam generation, and a bubble creation assembly 702 for generatingbubbles 718 in a stream fed into the FCRFLTC evaporator 640. In theFCRFLTV evaporator 640, the heating element 604 may be integrated withthe vapor drum 642, or may be separated therefrom but in fluidcommunication therewith, as described above.

As will be described in more detail later, bubbles 718 are generated byinjecting a suitable gas-phase substance 714 such as a non-condensablegas and/or a condensable gas or steam, into a stream to form bubbles 718therein. An example of non-condensable gas is hydrocarbon gas such asmethane, ethane, and the like. Suitable examples of condensable gasinclude vapor of a suitable solvent, such as liquefied petroleum gas,propane, and/or steam.

The heating element 604 comprises one or more vertical heating tubes 722forming a liquid channel for receiving feed water 712 and bubble-mixedwater stream 716 (described later) injected from the bottom thereof viaan inlet nozzle (not shown). A heating channel 724 on the outer surfaceof the vertical heating tubes 722 receives heat-exchange medium 610 suchas hot oil for heating the fluid in the heating tubes 722. After heatexchange, the temperature-reduced heat-exchange medium 612 is dischargedfrom the evaporator 600, and is reheated by an energy source (notshown).

The GIC evaporator 700 is to use gas bubbles 718 in combination with alarge blowdown circulation 652 and a pressure-letdown device 643 toeffectively mitigate and self-remove scales and other precipitates inthe evaporator 640.

In this embodiment, gas in a form of micro-bubbles 718, is mixed withboth the feed water 712 and the blowdown recirculation 652 in the bottomof the heating element 604, the bubble-mixed blowdown mixture then flowsupwards in the heating tubes 722 to fluidize and remove the precipitatesby contacting them with a large surface area of thick blowdown.

A pressure-letdown device 643 is installed on the top connection pipe646, to withhold water from flashing in the entire heating tubes 722.While fine scales, salts, and other precipitates may form in the topconnection pipe 646, particularly inside the throat of the pressureletdown device 643 due to the sudden flashing of the solution, bubbles718 therein are also squeezed to collapse creating cavitation toself-remove these precipitates in situ.

The pressure-letdown device 643 may be a throttling valve, an orifice, aconverging diffuser, or a converging-piping fitting. The pressure dropacross the pressure letdown device 643 may be optimized with theblowdown recirculation rate to obtain the evaporation-to-feed ratiorequired. Low pressure drop in combination with a high recirculationrate is always preferred as it leads to a mitigated scaling (i.e. byevaporation or induced by nucleation).

The energy needed for evaporation (flash) of the blowdown circulation isfrom both the hydraulic power of the pump 645 and the thermal heat inputto the heating element 604.

The steam/water mixture exits the top connection pipe 646 and enters thevapor drum 642 for both steam generation and separation.

A steam/liquid interface 648A is maintained in the vapor drum 642separating gas thereabove and liquid therebelow. In this embodiment, thesteam/liquid interface 648A is maintained at a level above its inletpiping system including the pressure letdown device 643 to allowflashing feed water into bulk liquid to further reduce the entranceturbulence and therefore, the nucleation scaling therein. The submergedentry also reduces salting as no super-saturation is generated.

A major portion 710 of the steam along with gas in equilibrium, isdischarged from the vapor drum 642 and co-injected into the reservoir102 for enhanced oil production.

In this embodiment, a small portion of the steam, denoted usingreference numeral 711, may be branched off and fed to thebubble-creation assembly 702 for bubble generation.

As shown in FIG. 13, the bubble-creation assembly 702 comprises asparger 704, a sparger pump 706, and a liquid source which in thisembodiment, is a steam condenser 708. The steam 711 is fed to the steamcondenser 708 to condense to water 709, which is then pumped to thesparger 704 via the sparger pump 706 for making clean sparger-motiveliquid 709.

The hydrocarbon gas in the steam 711 will be separated in the steamcondenser 708, and recovered in the produced gas or the vapor-recoverysystem (not shown) for use as fuel in the fired heater (508 in FIG. 11).

The sparger 704 receives the condensed water 709 and a high-pressure gasstream 714 such as hydrocarbon gas or other non-condensable gas orsteam.

Inside the sparger 704, the high-pressure gas 714 from the suction ofthe sparger flows through either a porous tube or an annulus, where itencounters the high speed motive water 709 and is sheared intomicro-bubbles 718. The bubble-mixed water stream 716 is then injectedinto the heating element 604.

FIG. 14 shows the circulation of bubble-mixed liquid between the heatingelement 604 and the vapor drum 642 in the GIC evaporator 640.

In this embodiment, a pressure-letdown device 643 is added to a priorart FCRFLTV to create a pressure drop of about 1.0 MPa to about 3.0 MPa.

The bubbles 718 enter the heating element 604 from bottom and moveupwards (indicated by arrows 701) inside the heating tubes 722. Thebubbles 718 then collapse inside the top connection piping 646 acrossthe pressure-letdown device 643 due to the contraction in the pipe.

There will be few bubbles after the letdown device 643, although gasremains in equilibrium with the high-pressure steam 710 and the blowdown649. moving up and down, respectively as shown.

Condensed vapor and un-vaporized liquid fall to a lower portion of thevapor drum 642 (indicated by arrow 649).

FIG. 15A is a schematic diagram of an HP GIC evaporator 740 having abubble pump and using condensed steam for bubble generation according toan alternative embodiment of this disclosure. The HP GIC evaporator 740disclosed herein may be used as the HP evaporator 424 in the process 400under the non-condensable gas co-injection, an enhanced oil recoverymethod for oil extraction.

The GIC evaporator 740 is similar to the evaporator 700 of FIG. 13except that in this embodiment, the evaporator 740 does not comprise asparger. Instead, the evaporator 740 comprises a bubble pump 742receiving water 709 from the condenser 708 and injecting gas 714 intothe casing of the pump 742 in which gas is sheared into high-densitymicro-bubbles for generating bubble-mixed water stream 716.

FIG. 15B is a schematic diagram of an HP GIC evaporator 750 using anexternal water source for bubble generation according to yet anotherembodiment of this disclosure. The HP GIC evaporator 740 disclosedherein may be used as the HP evaporator 424 in the process 400 under thenon-condensable gas co-injection, an enhanced oil recovery method foroil extraction.

The GIC evaporator 750 is similar to the evaporator 700 of FIG. 13except that, in this embodiment, the evaporator 750 does not use watercondensed from the evaporator vapor drum 642. Instead, water 752 from anexternal water source (not shown) is fed into the sparger 704 via asparger pump 706 for generating water stream 716 with micro bubbles 718mixed therein.

This scheme may be applicable when a portion, or all the evaporator feedwater 712, the evaporator make up water 442, and/or the recovered steamcondensate 532 is used for bubble generation.

FIG. 15C is a schematic diagram of an HP GIC evaporator 760 using theblowdown circulation and the solvent vapor for bubble generationaccording to still another embodiment of this disclosure.

The HP GIC evaporator 760 disclosed herein may be used as the HPevaporator 424 in the process 400 under the solvent-assisted oilextraction.

In this embodiment, solvent vapor 664 after being used for removal ofscales and other solids in situ in the evaporator 760, remains inequilibrium with the high pressure steam 710 thereafter and flows to thereservoir 102 to enhance the reservoir performance.

The GIC evaporator 760 is similar to the evaporator 750 of FIG. 15Bexcept that, instead of using an external water source andnon-condensable gas, the evaporator's blowdown circulation 652 and asolvent stream 664 are mixed in the sparger 704 to create a circulationstream 654 with solvent micro-bubbles 718 therein. The same arrangementcan be used for the non-condensable gas co-injection by replacing thecondensable solvent vapor 664 with a non-condensable gas.

As can be seen, the bubble-mixed blowdown stream 654 is combined withthe evaporator feed water 712 and fed into the heating element 604 fromthe bottom. The solvent bubbles 718 then flow upwards, interacting withscales and other solid precipitates and clean them in the same manner asthe non-condensable gas (see FIG. 13). Thus, the description of thecleaning process relates to the description of FIG. 13, and is notrepeated here.

In this embodiment, solvent 660 required for solvent-assisted extractionis pumped first into a solvent vaporizer 662 where it is heated,vaporized, and “self-compressed”to supercritical conditions with atleast pressure, or both pressure and temperature higher than itscritical point. The solvent at the supercritical conditions is thendelivered to the suction of the sparger 704 for bubble generation.

The solvent vaporizer 662 can be traditional shell and tube reboilertype, an intermediate fluid vaporizer type, or the like.

The blowdown recirculation pump 645 serves as both the blowdownrecirculation pump in the GIC evaporator 760 and the motive pump to thesparger 704.

In this embodiment, the blowdown recirculation 652 passes a sparger 704before the heating element 604. In an alternative embodiment, theblowdown circulation 652 is heated in the heating element 604 prior togenerating bubbles in a sparger 704. In various embodiments, the sparger704 is located upstream of the pressure-letdown device 643 in order tocollapse the bubbles 718 to clean precipitates in situ.

The solvent vaporizer 662 is arranged in a parallel arrangement with thecrystallizer heating element 521 and the optional produced waterpreheater 531, all receive heating supply from the heat-exchange mediumstream 518 at the outlet of the evaporator's heating element 604 (seeFIG. 16).

In this embodiment, the sparger 704 is at the highest elevation to allowdraining and purging the sparger with high pressure non-condensable gasbefore and after the shutdown to avoid plugging the sparger 704 when thesolvent vapor 664 is condensed, thereby creating vacuum and sucking inthe dirty blowdown.

Those skilled in art appreciate that both the high-pressure evaporator640 and the crystallizer 530 receive solvent bubbles. Furthermore,solvent bubbles may be generated using a water source other than theblowdown circulation 652, to allow the bubble mixed water to be injectedinto top of heating element 604, or into the inlet of top connectionpipe 646.

In FIG. 15C, a prior art FCRFLTV evaporator 640 is upgraded by addingthe bubble-creation assembly and the pressure-letdown device disclosedherein to make the FCRFLTV evaporator a fouling-resistant evaporator,capable of generating high-pressure steam in one step with no feed watersoftening. In some alternative embodiments, other suitable types ofevaporators may alternatively be used with the same upgrades to achievesimilar results. Such evaporators including but not limited to,forced-circulation falling-film evaporators, forced-circulatedrising/falling film evaporators, multiple-effect evaporators, and thelike, whether in a horizontal or a vertical orientation.

FIG. 16 is a plant wide heating and cooling medium system of process400, according to another embodiment of this disclosure.

In this embodiment, the high-temperature heat-exchange medium 506 from afired heater 508 is circulated to a high-pressure GIC evaporator 640 togenerate high-pressure injection steam 710. The heat-exchange medium 506gives up heat and exits the heating element 604 as stream 518.

The heat-exchange medium 518 with a reduced temperature is then pumpedto an organic Rankline cycle (ORC) power generator 550, in which thehigh-grade heat is converted to electricity at the best efficiencypossible as a consequence of the high temperature of about 240° C. toabout 300° C. maintained in stream 518.

The exhaust heat exchange medium 559 leaving the ORC 550 has atemperature of about 140° C.

In some embodiments, the ORC is in a parallel arrangement with otherprocess heaters such as the optional produced water preheater 531, thesolvent vaporizer 662, and the blowdown crystallizer 530.

The heat-exchange medium 559 at the exit of the ORC is recombined withthe exhausts from all its parallel heaters to form a hot medium stream562, cooled in a hot medium aerial cooler 557 to about 130° C., and usedfor cooling the inlet emulsion in the inlet-emulsion cooler 142.

The cold/hot medium, at 130° C., is also be used for cooling the inletproduced gas, for condensing the low pressure steam in the crystallizer530, and for heating the plant fuel gas supply.

The outflows from all the coolers and heaters are then recombined withthe remainder and excess of heat-exchange medium 583 to obtain arecombined stream 585. The excess heat-exchange medium 583 joins theoutflows via a cooling bypass 581.

In some embodiments, the recombined heat-exchange medium 585 is sent toan optional blowdown recirculation cooler 653 inside the GIC evaporator640.

The blowdown recirculation cooler 653 is an option if theconstructability of the blowdown recirculation pump 645 cannot match theoperating temperature required for the evaporator. Obviously, theblowdown recirculation cooler 653 can be omitted if an adequate pumpsuitable for corrosive and abrasive services can be sourced for hightemperature and high pressure ratings.

Again, the recombined heat-exchange medium 585 picks up heat from theblowdown concentrate recirculated 644, and exits the cooler at anelevated temperature. The temperature-elevated heat medium 587 thenreturns to the solar collector 510, or if a solar collector is not used,or if it does not exist, returns to the fired heater 508 for reheating.

A heat medium bypass 584 is used, to divert the excess heat-exchangemedium to the solar collector 510 or to the fired heater 508, in case oflow heating demand from the ORC 550 and its parallel heaters.

There is a heat medium expansion drum 588 at the suction of the heatmedium recirculation pump 512 to accommodate the volume increase, and tovent off entrained gas in the system.

The said heat medium expansion drum 588 can be shared with the coolingmedium system 580 through a restriction orifice 591 or equivalent, toalso provide expansion need for the cooling medium system. The coolingmedium loop uses the same heat transfer fluid as heat medium describedabove although they are operated at different temperature ranges.

The purpose of the cooling medium is to obtain and circulate alow-temperature cooling source of about 45° C. for recovery of producedgas, sales oil, low pressure steam, and for trim-cooling the inletemulsion. The cooling medium system is out of the scope of thisdisclosure, and its detail is omitted herein.

The method reverses the sequence of traditional heat integration byfirst tapping high-grade heat for power generation for the bestconversion efficiency, the temperature-reduced heat-exchange medium thenpicks up heat from the hot production and low pressure steam to recovermost of its initial enthalpy.

This method avoids a second heat transfer fluid such as glycol. In awinter shutdown, the fired heater 508 with a reduced output, wouldcontinue to produce both power and low grade winterization heat throughthe ROC, to further eliminate the winterization fired heater from theplant utility along with the diesel emergency power generator.

Although embodiments have been described above with reference to theaccompanying drawings, those of skill in the art will appreciate thatvariations and modifications may be made without departing from thescope thereof as defined by the appended claims.

What is claimed is:
 1. An evaporator for receiving a liquid stream andgenerating steam from the liquid stream, the liquid stream comprising atleast water, the evaporator comprising: a heating element comprising aliquid channel for receiving the liquid stream, and a heating channelfor directing a high-temperature heat-exchange medium therethrough toheat the liquid in the liquid channel via heat exchange between theheating channel and the liquid channel; a vapor drum for receiving theheated liquid from the heating element via a top connection pipe, andfor generating steam from the heated liquid, the vapor drum comprising asteam outlet for discharging generated steam, and a blowdown outlet fordischarging blowdown comprising un-vaporized liquid and impurities; abubble-creation assembly for generating bubbles using a gas-phasesubstance, and injecting generated bubbles into the heating element forself-removal of scales and other deposits in the evaporator; and awater/steam circulation path for recycling at least a portion of thesteam from the steam outlet of the vapor drum to a steam condenser forcondensation of the steam to produce a condensate which flows into thebubble-creation assembly for generating bubbles therein to create abubble-mixed water stream and feeding the bubble-mixed water stream intothe heating element.
 2. The evaporator of claim 1 further comprising: ablowdown recirculation cooler and a blowdown recirculation pump, forcooling and circulation of blowdown between the vapor drum and theheating element.
 3. The evaporator of claim 1 wherein the top connectionpipe comprises a pressure letdown device with reduced cross-section. 4.The evaporator of claim 3 wherein the pressure letdown device withreduced cross-section is a throttling valve, a restriction orifice, aconverging diffuser, or a converging piping fitting.
 5. The evaporatorof claim 1 wherein the bubble-creation assembly comprises a sparger, aneductor or a bubble pump.
 6. The evaporator of claim 1 wherein theheat-exchange medium is hot oil or synthetic heat transfer fluids. 7.The evaporator of claim 1 wherein the bubble-creation assembly comprisesa steam condenser for condensing the recycled steam into the motivewater stream.
 8. The evaporator of claim 1 further comprising a pipe teeon the blowdown outlet for splitting the blowdown into a blowdowncirculation stream and a blowdown discharge stream.
 9. The evaporator ofclaim 8 further comprising a successor crystallizer for receiving theblowdown discharge stream for further concentration of blowdown andrecovery of distillate.
 10. The evaporator of claim 9 wherein thecrystallizer comprises: a heating element, a flash drum, a sludgerecirculation pump, a steam condenser, a condensate sub-cooler, and atransfer pump.
 11. The evaporator of claim 9 wherein the crystallizercomprises a heating element configured for receiving a bubble mixedwater stream for self-removal of scales and other deposits therein. 12.The evaporator of claim 8 further comprising a return piping system fordirecting the blowdown circulation stream into the heating element. 13.The evaporator of claim 12 wherein the return piping system furthercomprises a blowdown recirculation pump for forcing the blowdowncirculation stream into the heating element.
 14. The evaporator of claim13 wherein the return piping system further comprises a blowdown coolerfor cooling the blowdown circulation stream.
 15. The evaporator of claim1 wherein the gas-phase substance is a non-condensable gas.
 16. Theevaporator of claim 1 wherein the gas-phase substance is a solvent vaporor other condensable gas vapors.
 17. The evaporator of claim 7 furthercomprising a heat-exchange medium circulation path for: heating theheat-exchange medium by a heating source and directing the heat-exchangemedium into the heating channel of the heating element; discharging theheat-exchange medium from the heating element; directing theheat-exchange medium to the steam condenser for condensing the recycledsteam into the motive water stream; directing the heat-exchange mediumto a blowdown recirculation cooler for cooling the blowdown, andreturning the heat-exchange medium discharged from the steam condenserand the blowdown recirculation cooler to the heating source.
 18. Theevaporator of claim 17 wherein the heat-exchange medium circulation pathis further configured for: directing the heat-exchange medium to aseries of heat exchangers for a plant wide heat integration beforedirecting the heat-exchange medium to the steam condenser and beforedirecting the heat-exchange medium to the blowdown recirculation cooler.19. The evaporator of claim 3 wherein the vapor drum is configured formaintaining a steam/liquid interface above the top connection pipethereof including the pressure letdown device.
 20. The evaporator ofclaim 1 wherein the bubble-creation assembly comprises a sparger forreceiving natural gas for generating the bubbles.
 21. The evaporator ofclaim 7 wherein the steam condenser is configured for separating gasfrom the recycled steam and discharging the separated gas.
 22. Theevaporator of claim 16 further comprising a solvent vaporizer forgenerating the solvent vapor in supercritical conditions.